Hundreds of serving Indian soldiers, including senior officers, are accused of involvement in widespread human rights abuses in Kashmir in a new report to be published on Thursday.

Many have been decorated and promoted despite serious allegations against them, the authors say. In a move likely to provoke anger, the report, by a team of veteran legal activists in the Himalayan state, names 500 "alleged perpetrators" ranging from low-ranking policemen to Indian army generals.

The charges relate to incidents occurring throughout more than 20 years of violence pitting armed religious and separatist groups against New Delhi's rule in Kashmir, and include shootings, abductions, torture and rapes.

The allegations will embarrass India, which takes great pride in being the world's largest democracy, and increase the pressure on local authorities to repeal emergency legislation implemented in Kashmir in 1990 at the beginning of the insurgency.

Though violence has subsided in recent years, in part due to warming relations with neighbouring Pakistan, which supported some insurgent groups, the Indian security establishment believes the potential for renewed conflict in Kashmir remains high.

The report is based on documents obtained under new freedom of information legislation, police statements, the government's own investigations and hundreds of interviews with family members and other witnesses. "Cases … reveal that there is a policy not to genuinely investigate or prosecute the armed forces for human rights violations. On the contrary, alleged perpetrators of crimes are awarded, rewarded and promoted," the report's authors said in a press statement. The report is published by the International People's Tribunal on Human Rights and Justice in Indian-administered Kashmir along with the Association of Parents of Disappeared Person.

Spokesmen from the Indian army and paramilitary forces deployed in Kashmir refused to comment on Wednesday.

The earliest incident covered in the report occurred in 1990, at the beginning of the conflict, when a 19-year-old student suspected of links to the growing militant movement in Kashmir was abducted by military personnel led by a major – named in the report – then tortured and killed. The report's authors were unable to find any evidence of any official investigation or disciplinary proceedings against the officer.

The worst of the violence occurred during the mid-1990s, when thousands of militants took on Indian security forces supplemented by locally hired irregulars. Human rights abuses were routine, with militants intimidating local communities and killing so-called spies while Indian authorities resorted to abduction, torture and extra-judicial execution on a wide scale. Sexual assaults on women were also common.

One incident from 1993 involved local police opening fire on peaceful, unarmed demonstrators and killing 35. No one has been disciplined despite a series of inquiries blaming police and describing how officials had attempted to cover up an "act of vengeance", the researchers found.

Other incidents in the 450-page report include a colonel paying off bereaved relatives after his unit used local villagers as human shields in a shootout with militants, scores of abductions and apparently random shootings designed to intimidate.

Specialised counter-insurgency units such as the Rashtriya Rifles feature repeatedly. In one incident in 2006, a "Major Rambo" and his men are accused of opening fire on children and youths fleeing after a suspected militant had been shot dead during a raid. Two 18-year-olds, a six-year-old and an eight-year-old were killed. The report notes that no police investigation was conducted. Military authorities blamed "terrorists" and "crossfire" for the deaths.

The most recent incident investigated by the authors of the report occurred in July last year, when a 28-year-old in the tense town of Sopore, a hotbed of militant activity, was arrested by a group of anti-terrorist police and soldiers on charges of possession of weapons. After several hours in police custody, Nazim Rashid Shalla telephoned his father to tell him he had been badly tortured and needed medical help, police documents and witness statements reveal.

His father was able to gain access to the police station, where he saw his semi-conscious son being beaten. Shalla died in custody the next morning.

Three constables have been suspended for their role in the death, but two senior officers named by the report as overseeing the arrest were awarded gallantry medals this year.

One frequent accusation is that Indian security forces in Kashmir have killed innocent civilians in staged gun battles and passed them off as separatist militants to earn rewards and promotions. One such alleged incident occurred in 2010, in which three labourers recruited to move arms and ammunition for the army were shot dead and then subsequently described as extremists who had crossed over from Pakistan. The report blames the killing on 11 people, including three Indian army officers. However, though three local informers have been detained, no others have been sanctioned as the case has become bogged down in legal battles. The Indian army maintains that servicemen must face a court martial not a civilian court.

Up to 70,000 people died in violence in Kashmir over recent decades, it is widely estimated. Civilians and security forces were killed in a series of suicide-style attacks and bombings. Such attacks justified the hardline often taken by security forces, former officers say. However, as the intensity of the conflict has ebbed in recent years, there has been a steady stream of revelations detailing abuses. In recent years, dozens of unmarked graves containing more than 2,000 corpses have been discovered on the Indian side of the line of control, the de facto border that has split the former kingdom between India and Pakistan for nearly 40 years.

A US diplomatic cable leaked by WikiLeaks and published by the Guardian in December 2010 revealed a briefing to the US embassy in Delhi in 2005 by representatives of the International Committee of the Red Cross (ICRC) which described continuing torture and arbitrary detention by security forces in Kashmir.

The dispatches, obtained by website WikiLeaks, revealed the ICRC's concerns about the use of electrocution, beatings and sexual humiliation against hundreds of detainees. Other cables show that as recently as 2007 American diplomats were concerned about widespread human rights abuses by Indian security forces, who they said relied on torture for confessions.

• This article was amended on 7 December 2012 to clarify the provenance of the report in question.